Yangtze River Source Region Research Articles

A novel framework for multiple thermokarst hazards risk assessment and controlling environmental factors analysis on the Qinghai-Tibet Plateau

Due to the influence of climate warming, the degradation of permafrost on the Qinghai-Tibet Plateau (QTP) has become evident. The formation of thermokarst hazards induced by the degradation of ice-rich permafrost has a significant impact on infrastructure construction and local ecology; therefore, it is necessary to assess its risk. Currently, high-precision and harmonized assessment tools for multiple thermokarst hazards risk assessment are lacking, and the mechanisms governing the environmental interactions of thermokarst hazards have not been fully clarified. In this study, a novel multiple thermokarst hazards risk assessment framework was proposed by combining stacking machine learning and potential environmental factors to assess the risk of thermokarst hazards in the Yangtze River source region (YRSR). In addition, model performance was improved by model optimization. Finally, structural equation modeling (SEM) was used to assess the controlling environmental factors for the thermokarst hazards in the YRSR. The results show that slope and precipitation contribute the most to the modeling accuracy of thermokarst lakes and thaw slumps, respectively. Model optimization improved the base model modeling accuracy by approximately 2 % ∼ 7 %, with XGBoost having the highest sensitivity to model optimization and the highest modeling accuracy. In terms of the ensemble strategy, the stacking model and ensemble model significantly improved the risk mapping accuracy, and the stacking model was better than the ensemble model, with accuracies of 92.39 % and 93.36 % for thermokarst lakes and thaw slumps, respectively. Compared with previous results, the results of this study are more representative of the YRSR. Finally, via SEM, terrain factors and soil factors were identified as controlling environmental factors for the risk of thaw slumps and thermokarst lakes, respectively. This study proposes a high-precision risk assessment method for thermokarst hazards in permafrost regions, and contributes to a deeper understanding of the interaction mechanisms between thermokarst hazards and environmental factors.

Predicting Seasonal Deformation Using InSAR and Machine Learning in the Permafrost Regions of the Yangtze River Source Region

AbstractQuantifying seasonal deformation is essential for accurately determining the thickness of the active layer and the distribution of water content within it, providing insights into the freeze‐thaw dynamics of permafrost environments and their sensitivity to climate change. Due to the limited hydraulic conductivity of the underlying permafrost, the freeze‐thaw processes are largely confined to the active layer, allowing for predictable seasonal deformations. This study employed Independent Component Analysis to isolate large‐scale seasonal deformation from Interferometric Synthetic Aperture Radar (InSAR) measurements taken from 2016 to 2020 in the Yangtze River Source Region (YRSR) of the Qinghai‐Tibet Plateau (QTP), covering 18,500 km2. We developed dedicated machine learning (ML) models that integrate these InSAR‐derived measurements with various environmental proxies. By applying these models to the YRSR, we generated a comprehensive, full‐coverage deformation map for permafrost terrains, achieving an R2 value of 0.91 and an Root Mean Squared Error of approximately 0.5 cm, thus confirming the model's strong predictability of seasonal deformation in permafrost regions. Deformation magnitude varied from less than 1 cm to over 10 cm. Our analysis suggests that terrain attributes, influenced by climate and soil conditions, are the primary factors driving these deformations. This research provides valuable insights into quantifying permafrost‐related seasonal deformation across expansive and rural landscapes. It also aids in assessing subsurface hydrological processes and the resilience and vulnerability of permafrost. The developed ML algorithm, with access to precise environmental data, is capable of forecasting seasonal deformations across the entire QTP and potentially throughout the Arctic.

Application of a Multi-Model Fusion Forecasting Approach in Runoff Prediction: A Case Study of the Yangtze River Source Region

Application of a Multi-Model Fusion Forecasting Approach in Runoff Prediction: A Case Study of the Yangtze River Source Region

A distributed modeling approach to water balance implications from changing land cover dynamics in permafrost environments

There is 78 % permafrost and seasonal frozen soil in the Yangtze River’s Source Region (SRYR), which is situated in the middle of the Qinghai-Xizang Plateau. Three distinct scenarios were developed in the Soil and Water Assessment Tool (SWAT) to model the effects of land cover change (LCC) on various water balance components. Discharge and percolation of groundwater have decreased by mid-December. This demonstrates the seasonal contributions of subsurface water, which diminish when soil freezes. During winter, when surface water inputs are low, groundwater storage becomes even more critical to ensure water supply due to this periodic trend. An impermeable layer underneath the active layer thickness decreases GWQ and PERC in LCC + permafrost scenario. The water transport and storage phase reached a critical point in August when precipitation, permafrost thawing, and snowmelt caused LATQ to surge. To prevent waterlogging and save water for dry periods, it is necessary to control this peak flow phase. Hydrological processes, permafrost dynamics, and land cover changes in the SRYR are difficult, according to the data. These interactions enhance water circulation throughout the year, recharge of groundwater supplies, surface runoff, and lateral flow. For the region’s water resource management to be effective in sustaining ecohydrology, ensuring appropriate water storage, and alleviating freshwater scarcity, these dynamics must be considered.

Evaluation of Ecological Sensitivity and Spatial Correlation Analysis of Landscape Patterns in Sanjiangyuan National Park

The Sanjiangyuan region, situated on the Qinghai–Tibetan Plateau, constitutes an exceptionally delicate ecological environment. Alterations in the region’s ecological landscape stem not only from natural factors but also from significant anthropogenic influences, exerting a notable impact on the sustainable economic and social development of the region’s middle and lower reaches. Consequently, investigating changes in the landscape pattern of Sanjiangyuan National Park holds paramount importance for comprehending the formation mechanism of spatial landscape distribution in the area. This study analyzes the ecological sensitivity and landscape pattern of Sanjiangyuan National Park in Qinghai Province, China, utilizing ArcGIS 10.8 and Fragstats 4.2. Employing the bivariate spatial autocorrelation analysis method, the research uncovers the spatial distribution characteristics between ecological sensitivity and landscape pattern, along with their aggregated change traits. The findings reveal that ecological sensitivity areas within the park encompass varying degrees, ranging from extremely sensitive to insensitive. The area of moderately sensitive zones in the Yellow River source region is 7279.67 km2 (39.17%), whereas the corresponding area in the Yangtze River source region is 32,572.34 km2 (36.30%). The eastern and northern parts of the Sanjiangyuan National Park exhibit significant landscape fragmentation. Ecological sensitivity varies markedly across different regions, with the southern and some northern areas showing higher sensitivity. In the Lancang River source park and the southern part of the Yellow River source park, the Largest Patch Index (LPI) and Ecological Sensitivity Index exhibit a high–high (HH) clustering pattern, indicating strong ecological connectivity in these areas. These regions also feature high Total Edge (TE), Number of Patches (NP), Patch Density (PD), and Edge Density (ED), indicating a complex landscape structure and abundant habitat edge areas. The study recommends restoring ecological connectivity in highly fragmented areas and implementing strict protection measures in sensitive regions to maintain ecosystem health and biodiversity. These findings provide a foundation for developing targeted ecological protection measures to enhance ecosystem health and biodiversity conservation in the area. This research aligns with several Sustainable Development Goals (SDGs), including Climate Action, Life on Land, and Clean Water and Sanitation, by promoting sustainable ecosystem management and biodiversity conservation.

Spatial Distribution Characteristics and Source Analysis of Ions in Lancang River and Yangtze River Source Region During Wet Period

Spatial Distribution Characteristics and Source Analysis of Ions in Lancang River and Yangtze River Source Region During Wet Period

Characteristics of Solar-Induced Chlorophyll Fluorescence in the Three River Headwaters Region, Qinghai-Tibetan Plateau during 2001 to 2020

The ecology of the Three River Headwaters Region (TRHR) is related to the long-term sustainable development of Qinghai Province and the whole of China. The change in chlorophyll fluorescence is an important index to measure the ecological environment. Therefore, it is of great significance to study the spatial and temporal distributions of Solar-induced chlorophyll fluorescence (SIF)and the related influencing factors in the TRHR. In this study, a high-resolution SIF dataset (2001–2020) was selected to be averaged on a time scale of years and months to investigate the annual and seasonal SIF characteristics, and the influencing climate factors were analyzed in combination with meteorological data by statistical method. The results showed that the SIF values ranged from 0.05 to 0.073 during 2001–2020, with a peak value of 0.073 in 2005 and 2009 and a minimum value of 0.05 in 2002. The averages of SIF values were higher in the source regions of the Yellow River source region (YR) and Langcang (Mekong) River source region (LCR) than in the source region of the Yangtze River source region (YZR). The SIF values of the TRHR in July, August and September were significantly higher than those in other months. The maximum value occurred in August at 0.11, and the minimum value was 0.008 in December. The precipitation had greater effect on the inter-annual variations in SIF. The monthly variation of SIF is influenced by precipitation, temperature and relative humidity. In addition, the influence of human activities and altitude on SIF should not be ignored. The results have certain reference value for protecting vegetation in the TRHR, and provide a reference for other regions to analyze the spatiotemporal changes and influencing factors by using SIF data.

Influence of alpine meadow deterioration on soil microbial communities in the Yangtze River source region

Introduction: Although soil microbial populations are a good predictor of soil texture, little is known about how they react to alpine meadow deterioration.Methods: This study utilized Illumina HiSeq sequencing to investigate the effects of alpine meadow degradation on soil microbial communities in the Yangtze River source basin at five different degradation levels [i.e., non–degraded (ND), slightly degraded (LD), moderately degraded (MD), severely degraded (SD), and very severely degraded (VD)].Results: The results indicated that bacterial and fungal α-diversity were not substantially different (p > 0.05) across the damaged alpine meadows, while β-diversity significantly differed (p < 0.01), indicating a higher variation in the microbial community due to alpine meadow degradation. Proteobacteria reduced considerably (p < 0.05) by 8.75%, 22.99%, and 24.65%, while Acidobacteria increased significantly (p < 0.05) by 41.67%, 85.20%, and 108.67%, in MD, SD, and VD compared with ND, respectively. Ascomycota declined significantly (p < 0.05) in the MD, whereas unclassified phyla rose significantly (p > 0.05) in the VD compared to the ND. The heatmaps of bacterial and fungal communities revealed two clusters: a ND, LD, and MD group and a SD and VD group, suggesting significant changes in soil microorganisms of alpine meadow in the SD and VD. Redundancy analysis (RDA) revealed that soil moisture, soil bulk density, soil organic carbon, total nitrogen, and plant biomass could explain 73.8% and 39.4% of the variance in bacterial and fungal community structure, respectively.Discussion: These findings imply that degradation of the alpine meadow impacts both plant and soil qualities, ultimately leading to changes in soil microbial populations in the Yangtze River’s source region.

Environmental Driving Factors and Assessment on the Aquatic Ecosystem of Periphytic Algae of Six Inflow Rivers in Yangtze River Basin

Phytoplankton is frequently utilized in the assessment of water ecological health, and a great number of related studies have been conducted in China; however, most of them are limited in scope. A phytoplankton survey was carried out at the basin scale in this study. A total of 139 sampling sites were set up in crucial locations of the main stream, from the Yangtze River's source region to the estuary, as well as the eight primary tributaries and the Three Gorges' tributaries. In the Yangtze River Basin, phytoplankton was found in seven phyla and 82 taxa, with Cryptophyta, Cyanophyta, and Bacillariophyta being the dominant species. To begin, the composition of phytoplankton communities in various sections of the Yangtze River Basin was studied, and LEfSe was utilized to identify highly enriched species in different regions. The association between phytoplankton communities and environmental factors in different sections of the Yangtze River Basin was then investigated using CCA. The generalized linear model demonstrated that TN and TP were strongly positively linked with phytoplankton density at the basin scale, whereas TITAN analysis identified the environmental indicator species and their corresponding optimal growth threshold range. Finally, the study assessed each Yangtze River Basin Region in terms of biotic and abiotic factors. Although the results of the two aspects were incongruent, the analysis of all indicators using the random forest method can yield comprehensive and objective ecological evaluation results for each section of the Yangtze River Basin.

Impact of climate change and land use change on ecosystem net primary productivity in the Yangtze River and Yellow River Source Region, China

Net ecosystem productivity (NEP) is an important indicator of the capacity of terrestrial ecosystems to absorb carbon. For the purpose of developing adaptation and mitigation strategies, it is essential to investigate the effect of climatic changes and anthropogenic activities on NEP. This study analyzed the spatiotemporal properties of NEP in the Yangtze River and Yellow River Source Region (SRYY) using remote sensing images, climate variable data, and land use data. Then it was examined at how climatic change affected carbon sinks and sources and how changes in land use affected carbon storage. According to the results, the SRYY contributed a carbon sink worth 35.26 Tg C annually from 2001 to 2019 (1 Tg = 1012 g). Influenced by climate, soil and vegetation, NEP displayed regional differences in space. The spatial distribution of NEP gradually increased from Northwest to Southeast. In recent twenty years, the NEP of SRYY slightly increased with a rate of 3.24 Tg C per decade. The NEP with an increasing trend accounted for 78.9% of the whole study area, which were widely distributed and especially significant in the west, such as Tuotuo River Basin. The correlation analysis between NEP and climate variables suggested that temperature was the dominant control of NEP in the SRYY. About 54.4% of the NEP variance across the entire SRYY was contributed by temperature. However, there was no significant linear relationship between NEP and annual precipitation. In recent two decades, built-up land expansion and ecological degradation reduced carbon sink by 28.61 Gg C (1 Gg = 109 g) and 1.94 Tg C, respectively. Grassland degradation caused by rodent infestation and grazing was the main factor of carbon sink reduction in some areas. The restoration of vegetation and wetland areas resulted in a 0.75 Tg C increase in the carbon sink. It might be benefited from warmer climate condition and ecological protection measures.

Riverine CO2 variations in permafrost catchments of the Yangtze River source region: Hot spots and hot moments

Rivers and streams are pivotal modulators in regional and global carbon cycles, but riverine CO2 flux is still uncertain for permafrost watersheds. Here we present the seasonal CO2 partial pressure (pCO2) and CO2 emission flux (FCO2) of 8 rivers and streams in the Yangtze River source region (YRSR), which have high permafrost coverage and seasonally thawed active layer. The YRSR rivers and streams are generally supersaturated with CO2, although there are a few sites with CO2 undersaturation during spring. The small headwater streams are CO2 hot spots that show significantly higher pCO2 (52 % higher) and FCO2 (792 % higher) than larger rivers. Both pCO2 and FCO2 show distinct seasonality across the study sites. pCO2 and FCO2 peak in summer and exhibit much lower levels in autumn and spring, indicating that hot moments of riverine CO2 occur in summer. Seasonal pCO2 and FCO2 variations are jointly controlled by hydrology, active layer dynamics and associated processes. The warm summer causes active layer thaw and highly active soil respiration, which release a large quantity of soil carbon and increase the CO2 sources via strengthened hydrologic connectivity. The high rainfall and more thaw-released water in summer bring high discharge, which can increase the water velocity and gas exchange rate and thus CO2 emission flux. Most of the variances of seasonal FCO2 (95 %) can be explained by hydrology and active layer thaw depth. Nevertheless, the hydrological process and seasonally thawed active layer over Qinghai-Tibet Plateau (QTP) play crucial roles in riverine carbon export due to the summer monsoon-dominated climate in QTP. Our results suggest that full seasonal coverage of CO2 dynamics is essential to quantify the annual CO2 flux accurately. Changing climate and warming permafrost may alter the annual CO2 emission due to deeper flow paths, hydrology changes, and longer emission windows throughout the year.

Variations in hydrological variables using distributed hydrological model in permafrost environment

The Yangtze River Source Region (YaRSR) is located in the third polar region, the most threatened zone by global warming after the Arctic. Permafrost covers eighty percent of the total area of YaRSR, while the rest is seasonally frozen ground. Due to a significant rise in air temperature, degradation of the permafrost could occur. Permafrost coverage in a river basin greatly controls its hydrology. This study focuses on hydrological modeling in this permafrost environment using the Soil and Water Assessment Tool (SWAT). The SWAT model was calibrated (1985–2000) and validated (2001–2015) on a daily time step. The results were also compared on a monthly time scale. An impermeable layer was introduced within the SWAT model to represent the permafrost conditions. The streamflow is strongly dependent on the seasonal variation of precipitation and temperature, and the rising limb of the hydrograph shows the melting of snow, the contribution of soil water, and thawing of permafrost during the spring-summer season. The permafrost layer well restricted the deep percolation of water. During the spring season, streamflow mainly consists of surface runoff because of the frozen soils. Permafrost and frozen ground thawing lead to an increase in the contribution of groundwater flow to streamflow. Ultimately, the frozen ground depletes as the temperature gets close to the freezing point. This study also describes the SWAT model application to better analyze and understand the hydrology of the permafrost/frozen ground with limited data availability.

Attribution of Changes in Streamflow to Climate Change and Land Cover Change in Yangtze River Source Region, China

The quantitative attribution of changes in streamflow to climate change (CC) and land cover change (LCC) for the Yangtze River Source Region (YRSR), China, was assessed. We used a combination of the SWAT model along with the statistical technique one factor at a time (OFAT) and innovative trend analysis (ITA) to achieve the study objectives. The climate and hydrology data from 1961 to 2016 and land-cover maps of 5 years’ difference from 1985 to 2015 were used. The model was calibrated (1964–1989) using a land-cover map of 1985 and validated for 1990–2016. This validated model was further validated for all other land-cover maps used in this study. The SWAT model simulation showed that streamflow had been significantly influenced by CC compared to LCC using land-cover maps of 1985–1990, 1990–1995. However, the SWAT model simulations did not result in further changes in streamflow for land cover maps of 2000–2005, 2005–2010, and 2010–2015 because there have not been any significant changes in land cover after 2000 while the main contributing factor was climate change. The SWAT model simulations showed that the main driver of changes in streamflow in the Yangtze River Source Region is climate change. This study shows that the individual impacts are more critical than combined impacts for designing hydraulic structures, water resources planning and management, and decision-making policies at the regional/basin scale.

Increasing annual streamflow and groundwater storage in response to climate warming in the Yangtze River source region

Climate warming has been driving hydrological changes across the globe, especially in high latitude and altitude regions. Long-term (1962–2012) streamflow records and permafrost data in the Yangtze River source region were selected to analyze streamflow variations and groundwater storage in response to climate warming. Results of Mann–Kendall test and Morlet wavelet analysis show that the anomalies of both annual streamflow and winter baseflow are near the year 2010, and their main period scales are 37 years and 34 years, respectively. The annual streamflow and the annual baseflow increased significantly, as assessed by the recursive digital filtering baseflow separation. Results of Pearson correlation coefficient indicate that the rising air temperature is the primary cause for the increased streamflow instead of precipitation and evaporation. By using the top temperature of permafrost model, the total permafrost area has decreased by 8200 km2 during the past 50 years, which causes groundwater storage to increase by about 1.62 km3 per year due to climate warming. More space has been made available to store the increasing meltwater during the permafrost thawing. Permafrost thawing and increasing temperature are the direct and indirect causes of the increasing groundwater storage. The results of the cumulative anomaly method and Pearson correlation coefficients show that permafrost thawing has a greater impact than increasing temperature on the increase of groundwater storage. Permafrost thawing due to climate warming show compound effects on groundwater storage–discharge mechanism, and significantly affects the mechanisms of streamflow generation and variation.

The Spatial-Temporal Variation Characteristics of Natural Vegetation Drought in the Yangtze River Source Region, China.

In the context of climate change, ecosystem in Yangtze River Source Region (YRSR) is under threat from severe droughts. This study introduced a new natural vegetation drought index, standardized supply-demand water index (SSDI), and identified natural vegetation drought events and parameters (e.g., duration, severity, peak, and coverage area) based on run theory. Then the drought-prone regions were investigated via 2-dimensional joint copula. The results indicate that (1) compared with traditional meteorological drought index, the SSDI is reliable and can reflect the comprehensive characteristics of the ecological drought information more easily and effectively; (2) the YRSR had witnessed the most severe drought episodes in the periods of late-1970s, mid-1980s, and mid-1990s, but the SSDI showed a wetting trend since the mid-2000s. Additionally, droughts in the Southern YRSR were relatively more severe with longer drought duration; (3) in most areas of Togton River Basin and Dam River Basin, the severe ecological drought events occurred more frequently; (4) drought duration and severity in the YRSR were more susceptible to temperature when the temperature rise was above 1.0 °C. The average drought duration and severity increased by 20.7% and 32.6% with a temperature rise of 1 °C. Investigating and evaluating drought characteristics, causes, and drought index effectiveness provide essential information for balanced water resource allocation, utilization, and drought prevention. Understanding these spatial-temporal characteristics of drought and return period was useful for drought risk assessment and sustainable development of water resources.

Local and geographical factors jointly drive elevational patterns of phytoplankton in the source region of the Yangtze River, China

AbstractLittle information about biodiversity patterns in high‐elevation aquatic systems has been gathered, even though these patterns are important for understanding the impacts of human activities. The source region of the Yangtze River, a typical alpine zone with vulnerable and sensitive ecosystems, was selected. Phytoplankton, which play a critical functional role as freshwater primary producers, serve as an important ecological indicator of aquatic systems. Here, systematic surveys on the water environment and phytoplankton were carried out to examine how the phytoplankton community varies with elevation based on hypothesized structural equation models (SEMs) in 10 typical rivers of the Yangtze River source region in March and October 2018. In total, 58 species of phytoplankton belonging to 28 genera were identified. The relationship between species abundance and elevation for phytoplankton showed unimodal elevational patterns. The results of the SEMs showed that all studied aspects affecting the phytoplankton community were directly or indirectly associated with elevation. The synergistic effects of human activities and basic environmental factors (terrestrial productivity and slope gradient) were the drivers affecting the phytoplankton community in the Yangtze River source region. Climate, topography, human activities and other factors are significantly different with changes in elevation, resulting in significant differences in the structure of aquatic communities at different elevations. Human activities were the major drivers affecting the phytoplankton community along the elevational gradient. As the elevation decreased, the disturbances to aquatic ecosystems caused by human activities intensified in the study area.

Characterization of the Recharge-Storage-Runoff Process of the Yangtze River Source Region under Climate Change

Storage and runoff are the two fundamental surface hydrological variables of a catchment. Research studies have been focused on the storage-runoff (S-R) hysteretic relationship of a catchment and its explanation very recently, thanks to satellite gravimetry. However, a complete analysis of a hydrological process starting from recharge to runoff has not been investigated. The S-R hysteretic relationship of Yangtze River Source Region (YRSR) situated in the northeast Tibetan Plateau is also unexplored. This study aims to investigate the Recharge-Storage-Runoff relationship of this catchment using gravimetrically-derived terrestrial water storage (TWS), satellite-derived and gauged precipitation, land surface modeled and gauged evapotranspiration, and runoff data measured during 2003–2012. We found that the Pearson correlation coefficient (PCC) of S-R relationship is 0.7070, in addition to the fact that the peak of runoff every year comes earlier than that of the storage. This finding enables us to further calculate equivalent runoff based on water balance equation using the above data, while comparing to measured runoff time series. The comparison of Global Land Data Assimilation System (GLDAS)-derived (gauge-derived) equivalent runoff against measured runoff reveals a PCC of 0.8992 (0.9402), respectively, indicating both storage and runoff are largely controlled by the recharge derived from precipitation and evapotranspiration. This implies the storage is not coupled with runoff prominently due to steep topography in YRSR unable to hold the water in the form of storage. Exceptional anomalous water storage time series in 2006 has also been investigated. We speculate that the low rainfall might partly be related to an El Niño Southern Oscillation event. The low rainfall and abrupt groundwater transfer are likely to be the causes of the anomaly in 2006.

Dynamic Changes of Plateau Wetlands in the Damqu River Basin, Yangtze River Source Region, China, 1988–2015

The assessment of wetland changes on the Tibetan Plateau (TP) is an important component of global change research. The Damqu River Basin (DRB) lies within the southern source of the Yangtze River and is part of the core wetlands area of the Three Rivers Source Region (TRSR). We examined the distribution of wetlands across this region based on remote sensing image interpretations. The results revealed clear evidence of changes over the period between 1988 and 2015, with the ​​wetland area in 2015 being 8964.51 km2 (53.52% of the total basin). Wetlands at this time were concentrated between 4700 and 5000 m (upper limit: 5600 m), with land slopes between 0 and 6°, and a northward aspect. The data also showed that the wetland area decreased by 71.16 km2 between 1988 and 2015, equivalent to 0.79% of the 1988 total. The annual value of the normalized difference vegetation index (NDVI) decreased over 63.36% of the region within the DRB during 1988–2015. The area of three major lakes in the DRB declined from 2009 to 2015. The results of this analysis demonstrated that precipitation variation was the underlying cause of the observed vegetation index and lake area changes within the DRB between 1988 and 2015.

Spatiotemporal Variability and Sources of DIC in Permafrost Catchments of the Yangtze River Source Region: Insights From Stable Carbon Isotope and Water Chemistry

AbstractRiverine dissolved inorganic carbon (DIC) exports play a central role in the regional and global carbon cycles. Here, we investigated the spatiotemporal variability and sources of DIC in eight catchments in the Yangtze River source region (YRSR) with variable permafrost coverage and seasonally thawed active layers. The YRSR catchments are DIC‐rich (averagely 25 mg C L−1) and export 3.51 g m−2 yr−1 of DIC. The seasonal changes of temperature, active layer, flow path, and discharge can alter DIC and stable carbon isotope of DIC (δ13C‐DIC). The most depleted δ13C‐DIC values were found in the thawed period, suggesting the soil‐respired CO2 during the active layer thaw period can promote bicarbonate production via H2CO3 weathering. Spatially, δ13C‐DIC values increased downstream, likely due to CO2 outgassing and changed permafrost coverage and runoff. We found that evaporite dissolution and silicate weathering in the seasonally thawed active layer contributed 44.2% and 30.9% of stream HCO3‐, respectively, while groundwater and rainwater contributed 16.7% and 7.3% of HCO3‐, respectively. Pure carbonate rock weathering played a negligible role in DIC production. These results were compatible with δ13C‐DIC source approximation results. Silicate weathering increased from initial thaw to thawed period, reflecting the active layer thaw and subsequent hydrology change impacts. Silicate weathering consumed 1.25 × 1010 mol of CO2 annually, while evaporite dissolution may produce CO2 and neutralize this CO2 sink. This study provides new understanding of the riverine DIC export processes of the YRSR. As permafrost degrades, the quantity, sources, and sinks of riverine DIC may also change spatiotemporally.

Historical and future changes of blue water and green water resources in the Yangtze River source region, China

The change of water resources resulting from climate warming in the Yangtze River Source Region (YRSR) has aroused wide concern in recent years. This research used the soil and water assessment tool (SWAT) to estimate the blue water (BW), green water flow (GWF), and green water storage (GWS). Then, the spatial and temporal change of BW, GWF, and GWS over the recent decades and next several decades was investigated. Results show that (1) the BW and GWF have increased by 2.3 mm/10a and 34.2 mm/10a from 1960 to 2012, while the GWG has decreased slightly by 0.19 mm/10a during the same period. (2) The spatial patterns of BW, GWF, and GWS have been changed obviously from 1980s to 2000s, especially for BW and GWF. The BW and GWF in the west and north of the YRSR where the water resource is relatively less are more sensitive to climate change; (3) the annual average temperature and precipitation in the YRSR are projected to increase by 2.2 °C and 9.8% during 2021 to 2050 compared to that during the 1961 to 1990. There is higher uncertainty in BW and GWS projection and the model-averaged BW and GWS would change little. The projected percent changes of GWF and GWS would be 15% and − 11.1% with less uncertainty. The obvious change of BW, GWF, and GWS in the future would occur in the west and north of the YRSR, which is similar with the spatial change in the historical period.